The more I think about this, the more I'm less inclined to think of the parents as completely without sympathy. My first reaction was "how could someone deny a person in agony a comforting bed!"
But according to the second update, not even the BF understood how much pain the GF was in. So how could the parents know?
Also, not knowing the degree of her discomfort, all we know is the BF suggested the GF stay another night. We don't know how strong that request was made. And according to the OP when he offered to advocate a second time after she learned of her major discomfort, she turned him down.
I know if I were in the GF's position I'd want to live a normal life and not overly share my medical problems or physical dicomfort. But I do think those in that position need to realize others do not automatically understand what they are going through. While we'd all like to be taken at our word, I think if we've never gone through something it is hard to truly understand. Like a migraine. Though I intellectually know that migraines and debilitating to many, I really do not understand to the depth of the pain they impose.
DH and I still laugh about my issue with smells during my first pregnancy. I had always been more prone to being bothered by odors and pregnancy just magnified it. During my first pregnancy, he and I worked within a few city blocks of each other and we'd commute together. The parking garage between our offices had a BBQ restaurant on the bottom floor and the smell made me ill each morning so he'd usually drop me off at my building and then go park. One morning he was running late for a meeting so drove directly to the garage though I warned him. As we were getting out of the car and he was handing me my laptop case I became ill on his shoes.
He learned to never question me again when I said a smell was making me nauseous. While a funny story, neither he nor I would have ever thought a woman who grew up in Texas could become physically ill by the smell of smoking meat.
So if someone said "oh my back is hurting" I'd assume to the degree I've had back aches unless more info was provided.